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Discussion Starter · #1 ·
I'll begin by apologizing for the long post. This is actually the short version.

I’m having a finishing problem that I just can’t seem to solve. I asked some questions about finishing a walnut coffee table last fall. Shortly after those postings I developed a severe case of Sciatica and was operated on in February. It’s been a long recovery but I’m finally back in the shop and trying to finish the coffee table top that I built last year.

My question, now in desperation, is how to proceed. In the two pictures you can see the unevenness of the finish when viewed under a raking light along the grain then the beautiful appearance when viewed under normal light across the grain.

I’m using Zar poly cut 50/50 with mineral spirits. I don’t know if that’s the right thing to do since I’m in Florida and the temp in my garage is mid to high 80’s when I apply the finish in the AM and it hit 90+ in the afternoon. I’m cutting it to make it a wiping poly and so that it dries faster and collects less dust. On the other hand I want to give it enough time to level and pop any bubbles. I don’t know if that’s the right way to do it.
Due to too many attempts to mention, I’ll just go over the last one which leads to the pictures. The Poly skinned over in the can even though I was using Bloxygen. I punched through the skin and ran a spoonful through cheese cloth. I then cut it with mineral spirits and applied it with a lamb’s wool applicator that I wrapped in a lint free paper towel to keep the wool from shedding into the finish. I ended up with a lot, and I mean a lot, of tiny nubs all over the table. I tried to take them down by using a 3M “Between Coats” finishing pad with my ROS. It wasn’t doing a great job so I used some 800 grit sandpaper which I believe is about the same grit as the sanding pad. Anyway, the result is what you see in the pictures. It is smooth as a baby’s butt, but doesn’t look good in a raking light. I did order a new can of Zar poly which will arrive next week.

Back to my question, how to proceed.

Do I need to do more sanding to the table top or will the next couple of coats of poly eliminate the blotches? I’m afraid to sand too much because, even with a high grit, I can sand down to the bare wood. I had 5 thinned coats on it before I started with the scotch brite pad and sandpaper.
Am I using the right ration of poly to mineral spirits based on the temperature? Should I be using more or less mineral spirits?

Am I applying the poly the best way? The paper towel around the lamb’s wool pad has made for a smoother application than a just a paper towel or a cloth.

So far, I’ve been playing around with this for a month, trying different approaches and I’ve already sanded back down to the bare wood and started over. Any suggestions will be gratefully accepted since this finishing job has me just about finished.
 

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Theo
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How many times do you expect people will be looking at it under a "raking" light? Sometimes close enough is good enough. You could always paint it.

I've got a small cherry wood bookcase I made in about 1953/4. Pretty sure the finish was varnish. It has held up beautifully.
 

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Barry, what I would do with that beautiful table is let it set a few days til the finish cures a little. Then get the set of Micromesh ROS pads and start with the 3000 grit and work up to the 12000 grit. You will be pleased with the "Porsche Fender" that you can see your face in and feels like a Steinway Piano. Follow with some Lundmark Carnuba Paste wax and buff out

https://www.amazon.com/Micro-Mesh-5-Disk-Assortment-Pack/dp/B003CLTREE

https://www.amazon.com/Lundmark-Wax-Paste-Clear-Lb/dp/B000BYAQC2

Herb
 

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What Herb said. You're probably spot on with the heat and humidity being a problem. But I agree that getting back to the finish too early in the cure is causing more problems.
A very light sanding to remove any dust specks, between coats, and then recoat.
In theory at least, sanding is removing the high spots and recoating is filling in the low spots, until it's all dead flat.
Check with the manufacture to see if they have any recommendations to extend the time allowable for the finish to self level!
 

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What Herb said. You're probably spot on with the heat and humidity being a problem. But I agree that getting back to the finish too early in the cure is causing more problems.
A very light sanding to remove any dust specks, between coats, and then recoat.
In theory at least, sanding is removing the high spots and recoating is filling in the low spots, until it's all dead flat.
Check with the manufacture to see if they have any recommendations to extend the time allowable for the finish to self level!
I have noticed that finishes tend to shrink as they cure and turn hard, this seems to also flatten out the surface.
Herb
 

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I have similar problems in temps over 80f. My summer weather is slightly hotter than Florida.
If I really need to complete the finish on a box in those temps, I put all the makings and the item in an air con room over night, set to 70f or less. Those 10 degrees make the difference between success and disaster.

Also, getting the stuff out of the workshop gets rid of all the floating dust that settles.

If you havent done much wipe on poly then the first coat should be very thin, wipe on, then with with a dry piece of cloth wipe off all excess. 24 hours to dry before repeating. If youre after a deep shine, 3 coats will work wonders.
 

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I never used to have problems with finishes until they starting making the quick dry stuff. I recently painted a night stand I made for my wife with paint I got from Benjamin Moore that had a 16 hour drying time and it turned out beautifully even though I came pretty close to getting runs in a few places when I sprayed it on. The slow drying time allows the paint to self level, something the quick dry stuff doesn't allow for as well.
 

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Strange coincidence. Our house here in Cyprus was painted from new with Benjamin Moore paint. Its an excellent product, we've had it repainted with the same and the decorator was amazed how well it spread and covered.
 

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I have similar problems in temps over 80f. My summer weather is slightly hotter than Florida.
If I really need to complete the finish on a box in those temps, I put all the makings and the item in an air con room over night, set to 70f or less. Those 10 degrees make the difference between success and disaster.

Also, getting the stuff out of the workshop gets rid of all the floating dust that settles.

If you haven't done much wipe on poly then the first coat should be very thin, wipe on, then with with a dry piece of cloth wipe off all excess. 24 hours to dry before repeating. If you're after a deep shine, 3 coats will work wonders.
Is it the heat or humidity that is the problem? I would be very suspect of high humidity slowing the curing process down substantially. The A/C lowers the temperature by removing the humidity. Of course A/C works a bit easier in places like Arizona:).
 

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I think Herb's advice is solid. The walnut looks beautiful and any finish used shouldn't cover that up but rather enhance it. I'd go with Herb's advice and see how that looks but I suspect highly it will be as wonderful as you expect it to be.
 

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Discussion Starter · #12 ·
Thank you all for your suggestions:

Theo, actually the table will be view daily under sort off a “raking” light. The table will be situated between a sectional and a 3 pane sliding glass door. When the sun is up, and it usually is in Florida, it will show the blotches if you’re sitting on the sectional looking across the table. That’s why I have the concern about the blotches. In my old home in PA, before I moved to FL, I wouldn’t care because, in that case, you’d be right. I do have some projects that I’ve completed with a “good enough for government work” mind set. This can’t be one of them

Herb, I bought a micromesh kit that contained small squares of all the grits. I used it on a name plaque that I had to repair after one of my grandsons broke his. After gluing I had to sand the whole front surface and I refinished it with the Zar 50/50 since I had it around. After it cured I micromeshed, if there is such a word, up to 6000 and it was so shiny that it looked like it was coated in plastic. Because the table will be used every day we decided on a semi-gloss finish. We think that gloss will show every tiny scratch. The semi might too, we’ll see. I do have some project in mind where I might go for the “grand piano” finish. First, I have to finish this %$#@#(* table top.

I never heard of the Lundmark wax. I have regular Johnson’s that I use on my cast iron surfaces, Briwax which I never really loved and don’t use it much and Renaissance wax which I have used on small projects with good success. I do like that the Lundmark contains carnauba wax. I add carnauba into my home made cutting board wax to add hardness. So, for a coffee table, that will get daily use, what wax would you recommend?

If I have to, I can bring the table into the house to finish it but I’m concerned about the solvent smell.

Dan, I’m taking your advice and will contact customer service at UGL, the manufacturer of ZAR and see what they suggest in terms of the mix, the temperature and humidity and the way I’m applying it. I will post any response I get since it might be useful to other forum members who live in hot and humid conditions.

Steve, thanks for your vote of confidence. I’ll try to live up to it.
 

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Is it the heat or humidity that is the problem? I would be very suspect of high humidity slowing the curing process down substantially. The A/C lowers the temperature by removing the humidity. Of course A/C works a bit easier in places like Arizona:).
Its actually the opposite, once the temps climb the wipe on poly dries as I'm applying it. it becomes lumpy and can not be smoothed or flattened in any way. Under 70f, it goes on smooth and finishes like glass.
 

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Barry, Johnsons Wax is fine, I like the Lundmark for the carnuba. Can't help you on the satin finish, I just sand the final coat with with 400g. and wax, the wax takes out any sanding marks.
 

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It's hard to tell from the photos, but what I saw in the raking light photo appears to be a haziness. If it's haziness, it's called blushing. It occurs in high humidity conditions. Moisture gets trapped in the finish, and the finish dries too much before it is released. Manufacturers of fine finishes (think auto paint), they make retarders, which are added to the paint to slow down drying time. I use a lot of clear CAB lacquer (I spray my finishes), but rarely have to use retarders because my shop is temperature controlled and humidity stay at a reasonable level.

I don't use brushes much, except for interior and exterior house painting, but you should be able to get a decent finish with a high quality brush. Thinning for a wipe on may be making blushing worse. A thinner coat drys faster than a thicker one. A very thin wipe on coat, coupled with high temperatures, may be causing the finish to dry too quickly and be unable to release the moisture. I suggest trying unthinned finish applied in full (but not heavy) coats applied with a brush.

By the way, you generally have to sand blush out. You should do your painting in a temperature controlled setting, like inside an air conditioned house. If you are intent on applying the finish at ambient temperature and humidity, the odds are high you are going to continue experiencing the same problem.

Gary
 

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It looks to me like you sanded through one or more layers of finish.
Since polyurethane does not "melt" previous coats, each layer is unique, and if you sand through it, you'll see it's edges.

If that's the case, then the only real fix is stripping it.
 

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Is it possible that the ROS sanding is heating up the finish causing it to blush...?

I would try hand sanding instead with a good flat block sander.

For applying the finish and to avoid bubbles, try wiping off the excess as soon as it is applied and between applications...? This might allow for less sanding between coats...?

Also try applying with something that might have less texture than a paper towel (depending on what you're using now). The texture might be creating the bubbles.
 

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I only ever use decent quality foam brushes and never go back over poly once I've completed a brush stroke (once in one direction, then a return stroke, and slightly overlap on the next brush stroke...then leave it alone!
Further to my comment earlier, maybe i will give Floetrol another try with polyurethane. Never really thought of it before this subject came up.
The downside to longer open time is that there's more opportunity for dust to get into the finish.
 

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I've seen hand sanding heat up a finish too. It'll start sticking to the paper. A hair dryer or heat gun will pop bubbles in a finish. Otis has said that he uses a propane torch for that. In any of those cases you might want to try a test piece first.
 

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I only ever use decent quality foam brushes and never go back over poly once I've completed a brush stroke (once in one direction, then a return stroke, and slightly overlap on the next brush stroke...then leave it alone!
Further to my comment earlier, maybe i will give Floetrol another try with polyurethane. Never really thought of it before this subject came up.
The downside to longer open time is that there's more opportunity for dust to get into the finish.
I've had problems with fast dry finishes even when spraying them. Some dry so fast when atomized that the surface feels pebbly to the touch. Lacquer works okay because the solvent melts into the previous coat but it doesn't work as well on water based finishes. I'll have to have a look at the Floetrol as a solution. As far as dust, it only takes maybe 1/2 an hour to build a frames and cover it with poly so that you can put the piece in it to cure. Build 3 sides with one side left open and you have a makeshift spray booth that keeps most of the finish off other things in your shop.
 
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